Spring Boot Logging with Logback SLF4J
Spring Boot uses SLF4J as logging API & Logback as default logging provider but also supports configuration for Log4j2 and Java Util logging frameworks. This Spring Boot logging example shows how to configure log levels in a Spring Boot application.
Step 1) Create application.properties file (under src/main/resources ) to set logging level. Note that root level logging level is the default logging level.
logging.level.root=INFO logging.level.com.example.demo=INFO logging.level.org.springframework.web=INFO
Step 2) Create SpringBootLoggingExample class
We will use SLF4J logging API to log the messages, so that we can switch to any logging framework like logback or log4j2 without any code changes. When run, SpringBootLoggingExample class will print logs with the level set in application.properties file.
package com.example.demo;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
@SpringBootApplication
public class SpringBootLoggingExample {
private static Logger logger = LoggerFactory.getLogger(SpringBootLoggingExample.class);
public static void main(String[] args) {
SpringApplication.run(SpringBootLoggingExample.class, args);
logger.trace("Spring Boot app started");
logger.warn("Spring Boot app started");
logger.info("Spring Boot Logging Example");
logger.debug("Spring Boot app starting"); }
} Step 3) Running SpringBootLoggingExample
To Run this Spring Boot application from command prompt, use following command → java -jar demo-0.0.1-SNAPSHOT.jar
Output :
2021-02-02 13:23:02.317 INFO 9304 --- [main] c.example.demo.SpringBootLoggingExample : Started SpringBootLoggingExample in 1.601 seconds (JVM running for 2.34) 2021-02-02 13:23:02.320 WARN 9304 --- [main] c.example.demo.SpringBootLoggingExample : Spring Boot app started 2021-02-02 13:23:02.321 INFO 9304 --- [main] c.example.demo.SpringBootLoggingExample : Spring Boot Logging Example
Step 4) Change logging level in application.properties to DEBUG and rerun the application.
You can play with the root level logging as per your logging requirements. Try to change it to ERROR, WARN, INFO, DEBUG and see the output.
logging.level.root=INFO logging.level.com.example.demo=DEBUG logging.level.org.springframework.web=INFO
Output :
2021-02-02 13:24:57.373 INFO 16084 --- [main] c.example.demo.SpringBootLoggingExample : No active profile set, falling back to default profiles: default 2021-02-02 13:24:58.248 INFO 16084 --- [main] c.example.demo.SpringBootLoggingExample : Started SpringBootLoggingExample in 1.421 seconds (JVM running for 2.121) 2021-02-02 13:24:58.253 WARN 16084 --- [main] c.example.demo.SpringBootLoggingExample : Spring Boot app started 2021-02-02 13:24:58.254 INFO 16084 --- [main] c.example.demo.SpringBootLoggingExample : Spring Boot Logging Example 2021-02-02 13:24:58.255 DEBUG 16084 --- [main] c.example.demo.SpringBootLoggingExample : Spring Boot app starting
Step 5) In case you want to write the logs to a file, then you need to change application.properties as shown below
logging.level.root=INFO logging.level.com.example.demo=INFO logging.level.org.springframework.web=INFO logging.file=application.log logging.path=/tmp/log
Using logback-spring.xml to configure logging
You can use application.properties for basic configuration, but if you want advanced logging configuration, then you need to create a logback-spring.xml file. Using xml file you can specify whether you want to log to console or a file by providing the appropriate appender. You can also specify the log pattern using pattern and can set the log level.
Create logback-spring.xml file (under src/main/resources) to set advanced logging configuration for production enviornment.
<?xml version="1.0" encoding="UTF-8"?>
<configuration>
<property name="HOME_LOG" value="logs/app.log"/>
<appender name="FILE-ROLLING" class="ch.qos.logback.core.rolling.RollingFileAppender">
<file>${HOME_LOG}</file>
<rollingPolicy class="ch.qos.logback.core.rolling.SizeAndTimeBasedRollingPolicy">
<fileNamePattern>logs/archived/app.%d{yyyy-MM-dd}.%i.log</fileNamePattern>
<maxFileSize>10MB</maxFileSize>
<totalSizeCap>10GB</totalSizeCap>
<maxHistory>30</maxHistory>
</rollingPolicy>
<encoder>
<pattern>%d [%thread] %-5level %logger{36} - %msg%n</pattern>
</encoder>
</appender>
<logger name="com.example.demo" level="debug" additivity="false">
<appender-ref ref="FILE-ROLLING"/>
</logger>
<root level="error">
<appender-ref ref="FILE-ROLLING"/>
</root>
</configuration> Log file Output (see app.log unders logs directory):
2019-10-27 16:23:41,954 [main] INFO c.e.demo.SpringBootLogbackExample - Starting SpringBootLogbackExample on ssss-PC with PID 5580 (C:\Dev\eclipse\workspace\SpringBoot\target\classes started by sss in C:\Dev\eclipse\workspace\SpringBoot)
2019-10-27 16:23:41,956 [main] INFO c.e.demo.SpringBootLogbackExample - No active profile set, falling back to default profiles: default
2019-10-27 16:23:43,597 [main] INFO o.s.b.w.e.tomcat.TomcatWebServer - Tomcat initialized with port(s): 8080 (http)
2019-10-27 16:23:43,622 [main] INFO o.a.coyote.http11.Http11NioProtocol - Initializing ProtocolHandler ["http-nio-8080"]
2019-10-27 16:23:43,640 [main] INFO o.a.catalina.core.StandardService - Starting service [Tomcat]
2019-10-27 16:23:43,640 [main] INFO o.a.catalina.core.StandardEngine - Starting Servlet engine: [Apache Tomcat/9.0.21]
2019-10-27 16:23:43,783 [main] INFO o.a.c.c.C.[Tomcat].[localhost].[/] - Initializing Spring embedded WebApplicationContext
2019-10-27 16:23:43,784 [main] INFO o.s.web.context.ContextLoader - Root WebApplicationContext: initialization completed in 1759 ms
2019-10-27 16:23:44,107 [main] INFO o.s.s.c.ThreadPoolTaskExecutor - Initializing ExecutorService 'applicationTaskExecutor'
2019-10-27 16:23:44,359 [main] INFO o.a.coyote.http11.Http11NioProtocol - Starting ProtocolHandler ["http-nio-8080"]
2019-10-27 16:23:44,392 [main] INFO o.s.b.w.e.tomcat.TomcatWebServer - Tomcat started on port(s): 8080 (http) with context path ''
2019-10-27 16:23:44,396 [main] INFO c.e.demo.SpringBootLogbackExample - Started SpringBootLogbackExample in 3.22 seconds (JVM running for 3.707)
Using another logging provider
Bu default, Spring Boot uses Logback as logging provider. You can also use another logging provider like Log4J2 or Java Util Logging. To use another logging provider, you first need to exclude spring-boot-starter-logger maven dependency which is provided as default by Spring Boot framework. After that you need to add the requied dependency like spring-boot-starter-log4j2. Since we use SLF4J as logging API, it will automatically pick up Log4J2 as logging provider as shown in below code.
private static Logger logger = LoggerFactory.getLogger(SpringBootLoggingExample.class);
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter</artifactId>
<exclusions>
<exclusion>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-logging</artifactId>
</exclusion>
</exclusions>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-log4j2</artifactId>
</dependency>